The invention relates to a method of checking cigarettes during the production or packaging of these cigarettes, a push rod being displaced axially in the direction of a cigarette end, with the result that, in the event of the incorrect formation or absence of a cigarette, the push rod assumes a position other than an ideal position. The invention also relates to a device for checking cigarettes for cigarette-packaging and/or cigarette-production machines, having at least one axially displaceably mounted push rod which has a head for penetrating into a cigarette end.
Methods and devices are known for checking cigarette ends using push rods, which are arranged in three layers and correspond to the geometry of a cigarette formation, said push rods being advanced up to a cigarette formation in order to check the cigarette ends. In the event of the correct formation of the cigarettes, in this checking operation, all the push rods are pushed into a rear position. However, if a cigarette is absent or if a cigarette is only loosely filled, the push rod remains in its starting position or is only pushed in to a slight extent. This operation of pushing in the push rods is usually checked by means of a light barrier provided for each layer. It is thus possible to infer from the pushing-in depth whether cigarettes are absent or defective. This checking method has the disadvantage that the light-barrier components become dirty over time. This may result in operational malfunctioning and thus in production being interrupted. Frequent maintenance of these installations is thus necessary.
The invention is thus based on the problem of improving the operation of checking cigarettes and of configuring this operation, in particular, such that it is less susceptible to malfunctioning.
In order to solve this problem, the method according to the invention is characterized in that an electric, magnetic or electromagnetic field assigned to a sensor is influenced in dependence on the position of the push rod, a signal which corresponds to the push-rod position being generated as a result of said field being influenced. The problem is also solved by a checking device according to the invention, which is characterized in that the push rod has a region for influencing an electric, magnetic or electromagnetic field assigned to a sensor, the sensor being designed such that it generates a signal which corresponds to the push-rod position as a result of said field being influenced. An advantage of the invention is that the checking method according to the invention or the checking device according to the invention is no longer susceptible to dust, since it is not based on an optical principle.
The position of the push rod is preferably determined by way of a depth to which a ferromagnetic and/or ferrimagnetic region of the push rod penetrates into the interior of a sensor-forming, in particular annular, coil. In this case, the coil is connected electrically to a measuring arrangement which emits a signal in dependence on the depth, representing the push-rod position, to which the ferromagnetic and/or ferrimagnetic region penetrates into the coil.
It is also preferred for the position of the push rod to be determined by way of a sensor-forming Hall element being magnetized by a magnetic field generated by a magnetic region of the push rod, it being the case that the Hall element is subjected to an electric voltage on two opposite sides and the signal is generated in dependence on the magnetic field, which magnetizes the Hall element and represents the push-rod position. Here too, the Hall element is preferably connected to an electric measuring arrangement which emits a signal in dependence on the magnetic field, which magnetizes the Hall element and represents the push-rod position.
The advantage of these preferred solutions is that they are small enough in order to be able to sense each cigarette of a relatively large cigarette formation at the same time. By virtue of the invention, it is then no longer necessary for cigarettes to be checked at different locations or times. This is because the devices according to the invention may be small enough for the necessary measuring arrangements, namely Hall elements or coils, not to be larger than the thickness of a cigarette. In particular, the coils thus have an external diameter which is smaller than a cigarette diameter.
It is preferable, during a checking operation, for all the cigarettes of a cigarette formation fed to a cigarette pack to be checked at the same time, the individual push-rod positions being evaluated individually, with the result that systematic faults can be detected. The latter include, in particular, such faults as occur in the case of adjacent cigarettes or cigarette positions which are located in different layers one above the other. It is thus possible to detect, for example, a defective cigarette shaft. In the event of such a fault, finally, an alarm or control signal is generated in order to reduce the rotational speed of a packaging and/or production machine, or in order to stop the same.
The push rods are preferably interrogated individually. For this purpose, each push rod is assigned an element which can be interrogated individually, namely a Hall element or an, in particular, annular coil. The signals emitted by these elements are evaluated by means of an evaluation unit. This evaluation unit is small enough to be accommodated in the housing of the checking device, with the result that it is advantageously possible to dispense with high-outlay wiring of all the individual elements to a central machine-control means.